The present invention relates generally to the television receiving art and more particularly to the recognition of noisy or weak signal conditions in the received signal.
The N.T.S.C. regulates transmitted television signals as to their timing and the duration of particular subparts of the total transmitted signal. In particular, the N.T.S.C. regulations call for the transmission of vertical and horizontal sync information to be used by the receiver for synchronizing the horizontal and vertical sweep of the display screen in a raster-like fashion. In an ideal environment, the television receiver is responsive only to this synchronizing information which is carried on the transmitted signal and effectively coordinates the horizontal and vertical sweep of the display screen.
However, a television receiving system is seldom operated in an ideal environment. Typically, the transmitted signal is subjected to noisy static type conditions caused by extraneous electrical discharges and to attenuation due to atomospheric conditions and the distance over which the signal must travel. Quite frequently, the received signal is lacking in either signal strength or the synchronizing information or both. Without these it is difficult to produce a jitter-free display which is comfortable to watch.
Accordingly, it is desired to provide improved means for recognizing when a received television signal lacks the necessary characteristics to produce a sufficiently coordinated display comfortable for the ordinary viewer. It is also desired that such means operate in a fashion compatible with the remainder of the receiving circuitry and efficiently and advantageously make use of the signals which are normally available inside a television receiving set. Additionally, it is desired that the signal recognition means be durable, dependable, and of relatively low cost.
Therefore, it is a primary object of the present invention to provide a means and method for analyzing the sync characteristics of received signals to recognize signals which are too weak for providing an acceptable displayed picture and to provide for compensation for such signals to create an acceptable displayed picture.
It is an additional object of the present invention to provide for the compatibility between a recognition system and existing methods and systems within a television receiver.
It is still a further object of the present invention to provide dependable, durable and cost efficient means and method for recognizing weak signals.